Iron oxide coated substrates

ABSTRACT

Processes for coating substrates, in particular substrates including shielded surfaces, with iron oxide-containing coatings are disclosed. Such processes comprise contacting a substrate with an iron oxide precursor, preferably maintaining the precursor coated substrate at conditions to equilibrate the coating, and then oxidizing the precursor to form a substrate containing iron oxide. Also disclosed are substrates coated with iron oxide-containing coatings for use in various magnetic applications.

RELATED APPLICATIONS

This application is a division of application Ser. No. 07/743,827, filedAug. 12, 1991, U.S. Pat. No. 5,290,589 which is a continuation in partof application Ser. No. 621,660 filed Dec. 3, 1990 now U.S. Pat. No.5,204,140, which application in turn is a continuation-in-part ofapplication Ser. Nos. 348,789 now U.S. Pat. No. 5,167,820; 348,788 nowU.S. Pat. No. 5,039,845; 348,787 now abandoned and 348,786 now U.S. Pat.No. 5,182,165, each filed May 8, 1989, each of which applications is acontinuation-in-part of application Ser. Nos. 272,517 and 272,539, eachfiled Nov. 17, 1988 now abandoned, each of which applications in turn,is a continuation-in-part of application Ser. No. 082,277, filed Aug. 6,1987 (now U.S. Pat. 4,787,125) which application, in turn, is a divisionof application Ser. No. 843,047, filed Mar. 24, 1986, now U.S. Pat. No.4,713,306. Each of these earlier filed applications and these U.S.Patents is incorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a process for coating a substrate. Moreparticularly, the invention relates to coating a substrate with a ironoxide-containing material, preferably a magnetic iron oxide-containingmaterial.

An application where substrates with coatings, e.g., magnetic conductivecoatings, find particular usefulness is memory cores, linear, power andrecording head application, magnets and heating.

In many of the above-noted applications it would be advantageous to havea magnetic iron oxide which is substantially uniform, has highpermeability, and has good chemical properties, e.g., morphology,stability, etc.

A number of techniques may be employed to provide conductive iron oxidecoatings on substrates. Most ferrites are prepared as ceramic materialsby standard ceramic processing. In this process the constituent rawmaterials, oxides, hydroxides, or carbonates, are weighed and firstmilled in a steel mill using steel balls as the milling media and wateras the carrier. During milling, the raw materials are mixed to yield ahomogeneous mixture. Other mixing methods may also be employed such asdry mixing of raw materials. The milling gives uniform mixing andresults in some size reduction leading to better reactivity in thecalcining step. In the calcining (sometimes called presintering)reaction, the raw materials are heated to 800° to 1300° C. and form theferrite compound. The carbonates decompose and react by solid-statediffusion to form the final compound.

In the case of the nickel-zinc-spinel ferrites, the powder is calcinedat a temperature of ca 1027° C. to yield an agglomerated, friable powderthat is essentially 100% converted to the spinel phase. However, in thecase of the manganese-zinc-ferrites, the calcining conditions are suchthat the material is 50-85% converted to spinel. Time and temperatureare the most important control parameters in the calcining step.

The purpose of this millings is to further homogenize the material andto reduce the particle size to permit subsequent pressing and sintering.The milling itself can be carried out in a variety of ways, for example,wet-ball mill with steel balls in a manner analogous to the firstmilling. The main objective is to get a finely divided powder that canbe slurried and spray dried.

Following the second milling, the material must be granulated so that itwill be free flowing and can be dry pressed into the desired shape. Amethod for producing ferrite powder is to add a binder such aspoly(ethylene glycol) or poly(vinyl alcohol) at 1-4 wt % and sufficientwater for form a slurry that is about 65-70 wt % ferrite. The slurry isspray dried to yield a dry powder consisting of small sphericalparticles having a narrow size distribution.

Very thin parts, such as used in memory cores, may be formed by tapecasting followed by punching the desired shape. Parts that have a highlength-to-diameter ratio may be formed by either extrusion or byisostatic pressing.

In the sintering process, the ceramic material is densified and thefinal magnetic properties are developed. Some materials such as theiron-deficient nickel-zinc=ferrites and the M-type hexagonal ferritesmay be fired in air because all the cations exist at their highestvalence state. However, with the manganese-zinc ferrites the amount offerrous iron (Fe²⁺) in the crystal lattice is controlled. Typicaltemperatures for the sintering zone are in the range of 1275°-1450° C.;sintering time may range from 20 minutes to 12 hours.

The next zone in the kiln is called the anneal or equilibration zone,where the temperature is dropped to 1000°-1300° C. and the oxygencontent of the atmosphere is lowered by the introduction of nitrogengas. At this elevated temperature the ferrite equilibrates quickly withthe atmosphere, and the desired ferrous iron level is established.Following the annealing step, the parts are cooled as rapidly aspossible and the oxygen content of the atmosphere is reduced stillfurther.

In an attempt to improve chemical homogeneity, a wet-chemical processwas designed in which an aqueous solution was prepared containing themetal cations. Addition of a strong base (e.g., NaOH) precipitated anintermediate hydroxide which was subsequently oxidized by bubbling airthrough the suspension. The results was a homogeneous fine-particleferrite. A similar type of process used an ammonium bicarbonate-ammoniumhydroxide mixture as the precipitating agent followed by conventionalcalcining.

The preparation of ferrite compounds by the cryochemical method has alsobeen investigated. In this technique, an aqueous solution is sprayedinto a chilled liquid (e.g., hexane) where the droplets freeze intobeads ca), 0.4 mm diameter. These pellets are removed from the liquidand placed in a freeze dryer where the moisture is removed bysublimation. The resultant pellets are converted to the spinel bycalcining.

The preparation of the hexagonal ferrites by wet-chemical precipitation,topotactic reaction, and fluidized-bed reaction has been investigated.However, the most common method is standard ceramic processing.

Critical areas of process control in the conventional type processingare the composition and the presintering conditions. The calcining stepis especially critical because it determines to a large extent theproperties of the magnet after sintering. At a typical calciningtemperature of 1300° C. the material reacts completely to form thehexagonal phase. If calcining takes place at a lower temperature, themagnetic properties are not affected adversely but the calcined materialis too soft and the subsequent milling step which gives a very fineparticle size. This leads to difficulty in pressing and a very highshrinkage during sintering. If, on the other hand, the sinteringtemperature is too high, the particles are too hard and the particlesize after milling is rather coarse. Although this does not cause apressing problem, after sintering the particles are too large and theshrinkage and coercive force are both too low.

After calcining the material must be milled to reduce the particle sizeto the range of 1 μm in order to obtain single-domain properties.

Fabrication of the milled powder into parts can take place by a numberof methods depending on the degree of magnetic alignment desired. Forthe lowest-grade material, the milled powder is spray dried and then drypressed into the required shape. In these materials, the individualparticles are randomly aligned with respect to each other, resulting ina isotropic magnet in which the magnetic properties are the same in alldirections.

Anisotropic magnets are prepared by dry or wet pressing the material inthe presence of an external magnetic field which causes the individualmagnetic particles to align themselves with that field. The dry-pressingtechnique is quite similar to that used for preparing isotropic magnets,except that pressing takes place in the presence of a magnetic field.

Wet pressing, gives the highest degree of alignment with the fieldbecause the individual particles are much freer to rotate under itsinfluence. When alignment is essentially complete, the water is removedby applying a vacuum to the die cavity, and a very fine filter paperprevents the powder from being pulled out with the water.

Sintering of dry-pressed parts can take place immediately after forming.However, wet-pressed parts must be carefully dried to remove most of theresidual moisture before being placed in the kiln. Drying undercontrolled conditions may take from 10 to 200 hours, depending on sizeand shape.

The pressed parts are sintered in the air at 1125°-1375° C. to yield adense ceramic material. In order to minimize the grain growth thatoccurs during sintering, the firing temperature is kept as low aspossible.

Conventional processing has been used for the preparation of powder forfollow on consolidation into final shapes. Such processing has not beendirected at or concerned with thin and/or thick films and a wide varietyof inorganic substrates, the Novel components and articles produced orthe unique properties of such coated components in a wide variety ofapplications.

One of the preferred substrates for use in certain magnetic mechanicaldevices are inorganic substrate, in particular flakes, spheres, fibersand other type particles.

SUMMARY OF THE INVENTION

A new process for at least partially coating a substrate with a ironoxide-forming material has been discovered. In brief, the processcomprises contacting the substrate with a iron oxide precursor, forexample, an iron chloride precursor such as ferric chloride thehexahydrate thereof here in after referred to as iron chloride precursorin a vaporous form and/or in a liquid form and/or in a solid (e.g.,powder) form, to form a iron oxide precursor-containing coating, forexample, a iron chloride-containing coating, on the substrate;preferably contacting the substrate with an additional magnetic and/orproperty enhancing interacting and/or dopant components, i.e., aninteracting component containing for example nickel, zinc, manganese,barium, strontium, lead, calcium, boron, titanium, silica yttrium,lanthanum and the rare earths (as in a compound), to form a interactingcomponent-containing coating on the substrate; and contacting the coatedsubstrate with an oxidizing agent to form a iron oxide-containing,coating on the substrate. The contacting of the substrate with the ironoxide precursor and with the interacting component can occur together,i.e., simultaneously, and/or in separate steps.

This process can provide coated substrates which have substantialmagnetic permeability so as to be suitable for use as components inmagnetic type elements, articles and applications. Substantial coatinguniformity, e.g., in the thickness of the iron oxide-containing coatingand in the distribution of dopant component in the coating, is obtained.Further, the present doped iron oxide coated substrates have outstandingstability, e.g., in terms of magnetic and mechanical properties andmorphology, and are thus useful in various applications. In addition,the process is efficient in utilizing the materials which are employedto form the coated substrate.

DETAILED DESCRIPTION OF THE INVENTION

In one broad aspect, the present coating process comprises contacting asubstrate with a composition comprising an iron oxide precursor, such asiron chloride precursor and hydrates, iron organic and complexes, ironsulfate hydrates and mixtures thereof, preferably ferric chloride andhydrates, at conditions, preferably substantially non-deleteriousoxidizing conditions, more preferably in a substantially inertenvironment or atmosphere, effective to form a iron oxideprecursor-containing coating, such as a iron chloride-containingcoating, on at least a portion of the substrate. The substrate ispreferably also contacted with at least one interacting component,as setforth at conditions, preferably substantially non-deleterious oxidizingconditions, more preferably in a substantially inert atmosphere,effective to form a interacting forming component-containing coating,such as a nickel, zinc, and manganese or zinc and yttrium and gadoliniumcomponent-containing coating, on at least a portion of the substrate.This substrate, including one or more coatings containing iron oxideprecursor, for example ferric chloride and the hexahydrate andpreferably an interacting-forming component, is contacted with at leastone oxidizing agent at conditions effective to convert the iron oxideprecursor to iron oxide and form a iron oxide-containing coating,preferably with an interacting nickel/zinc and/or manganese/zinc on atleast a portion of the substrate. By "non-deleterious oxidation" ismeant that the majority of the oxidation of iron oxide precursor, forexample ferric chloride, coated onto the substrate takes place in theoxidizing agent contacting step of the process, after distribution,and/or equilibration of the precursor rather than in process step orsteps conducted at non-deleterious oxidizing conditions. The process asset forth below will be described in many instances with reference toferric chloride including its hexahydrate which has been found toprovide particularly outstanding process and product properties. Thehexahydrate is preferred for process temperatures below 300° C. althougha compatible solvent system for ferric chloride can also be used.However, it is to be understood that other suitable iron oxideprecursors are included within the scope of the present invention.

The interacting-forming component-containing coating may be applied tothe substrate before and/or after and/or during the time the substrateis coated with iron chloride. In a particularly useful embodiment, theiron chloride and the interacting-forming component are both present inthe same composition used to contact the substrate so that the ironchloride-containing coating further contains the interacting-formingcomponent. This embodiment provides processing efficiencies since thenumber of process steps is reduced (relative to separately coating thesubstrate with iron chloride and interacting-forming component). Inaddition, the relative amount of iron chloride and dopant-formingcomponent used to coat the substrate can be effectively controlled inthis "single coating composition" embodiment of the present invention.

In another useful embodiment, the substrate with the ironchloride-containing coating and the interacting-formingcomponent-containing coating is maintained at conditions, preferably atsubstantially non-deleterious oxidizing conditions, for example,conditions which reduce and/or minimize the formation of iron oxide on arelatively small portion of the substrate or off the substrate, for aperiod of time effective to do at least one of the following: (1) coat alarger portion of the substrate with iron chloride-containing coating;(2) distribute the iron chloride coating over the substrate; (3) makethe iron chloride-containing coating more uniform in thickness; and (4)distribute the interacting-forming component more uniformly in the ironchloride-containing coating. Such maintaining preferably occurs for aperiod of time in the range of about 0.05 or 0.1 minute to about 20minutes in the presence of an inert gas and/or oxygen i.e. air, undernon-deleterious oxidizing conditions. Such maintaining is preferablyconducted at the same or a higher temperature relative to thetemperature at which the substrate/iron chloride-containing compositioncontacting occurs. Such maintaining, in general, acts to make thecoating more uniform and, thereby, for example, provides for beneficialelectrical conductivity properties. The thickness of the ironoxide-containing coating is preferably in the range of about 0.1 micronto about 100 microns, more preferably about 1 micron to about 50microns.

The iron chloride which is contacted with the substrate is in a vaporousphase or state, or in a liquid phase or state, or in a solid state orphase (powder) at the time of the contacting. The composition whichincludes the iron chloride preferably also includes theinteracting-forming component or components. This composition may alsoinclude one or more other materials, e.g., dopants, catalysts, graingrowth inhibitors, solvents, etc., which do not substantially adverselypromote the premature hydrolysis and/or oxidation of the iron chlorideand/or the interacting-forming component, and do not substantiallyadversely affect the properties of the final product, such as by leavinga detrimental residue in the final product prior to the formation of theiron oxide-containing coating. Thus, it has been found to be important,e.g., to obtaining a iron oxide coating with good structural, mechanicaland/or magnetic properties, that undue hydrolysis of the iron chlorideand interacting-forming component be avoided. Examples of useful othermaterials include organic components such as acetonitrile, ethylacetate, dimethyl sulfoxide, propylene carbonate and mixtures thereof;certain inorganic salts and mixtures thereof. These other materials,which are preferably substantially anhydrous, may often be considered asa carrier, e.g., solvent, for the iron chloride and/or dopant-formingcomponent to be contacted with the substrate. It has also been foundthat the substrate can first be contacted with a iron oxide precursorpowder, particularly iron chloride powder, preferably with a filmforming amount of such powder, followed by increasing the temperature ofthe powder to the liquidus point of the powder on the substrate andmaintaining the coated substrate for a period of time at conditionsincluding the increased temperature effective to do at least one of thefollowing: (1) coat a larger portion of the substrate with the ironoxide precursor-containing coating; (2) distribute the coating over thesubstrate; and (3) make the coating more uniform in thickness.Preferably, this step provides for the equilibration of the coating onthe substrate. The size distribution of the powder, for example, ironchloride powder, and the amount of such powder applied to the substrateare preferably chosen so as to distribute the coating over substantiallythe entire substrate.

The iron oxide precursor powder can be applied to the substrate as apowder, particularly in the range of about 5 or about 10 to about 125microns in average particle size the size in part being a function ofthe particle size, i.e. smaller particles generally require smaller sizepowders. The powder is preferably applied as a charged fluidized powder,in particular having a charge opposite that of the substrate or at atemperature where the powder contacts and adheres to the substrate rate.In carrying out the powder coating, the coating system can be, forexample, one or more electrostatic fluidized beds, spray systems havinga fluidized chamber, and other means for applying powder, preferably ina film forming amount. The amount of powder used is generally based onthe thickness of the desired coating and incidental losses that mayoccur during processing. The powder process together with conversion toa iron oxide-containing coating can be repeated to achieve desiredcoating properties, such as desired gradient conductivities.

Typically, the fluidizing gaseous medium is selected to be compatiblewith the iron oxide precursor powder, i.e., to not substantiallyadversely affect the formation of a coating on the substrate duringmelting and ultimate conversion to a iron oxide-containing film.

Generally, gases such as air, nitrogen, argon, helium and the like, canbe used, with air being a gas of choice, where no substantial adverseprehydrolysis or oxidation reaction of the powder precursor takes placeprior to the oxidation-reaction to the iron oxide coating as previouslydiscussed under equilibration and maintaining. The gas flow rate istypically selected to obtain fluidization and charge transfer to thepowder. Fine powders require less gas flow for equivalent deposition. Ithas been found that small amounts of water vapor enhance chargetransfer. The temperature of the powder precursor is generally in therange of about 0° C. to about 100° C., or higher more preferably about20° C. to about 40° C., and still more preferably about ambienttemperature. The substrate however, can be at a temperature the same as,higher or substantially higher than the powder.

The time for contacting the substrate with precursor powder is generallya function of the substrate bulk density, thickness, powder size and gasflow rate. The particular coating means is selected in part according tothe above criteria, particularly the geometry of the substrate. Forexample, particles, spheres, flakes, short fibers and other similarsubstrate, can be coated directly in a fluidized bed themselves withsuch substrates being in a fluidized motion or state. For fabrics androvings a preferred method is to transport the fabric and/or rovingdirectly through a fluidized bed for powder contacting. In the case ofrovings, a fiber spreader can be used which exposes the filaments withinthe fiber bundle to the powder. The powder coating can be adjusted suchthat all sides of the substrate fabric, roving and the like arecontacted with powder. Typical contacting time can vary from seconds tominutes, preferably in the range of about 1 second to about 120 seconds,more preferably about 2 seconds to about 30 seconds.

Typical iron oxide precursor powders are those that are powders atpowder/substrate contacting conditions and which are liquidus at themaintaining conditions, preferably equilibration conditions, of thepresent process. It is preferred that the powder on meltingsubstantially wets the surface of the substrate, preferably having a lowcontact angle formed by the liquid precursor in contact with thesubstrate and has a relatively low viscosity and low vapor pressure atthe temperature conditions of melting and maintaining, preferablymelting within the range of about 300° C. to about 450° C., or higher,more preferably about 350° C. to about 300° C. Typical powder iron oxideprecursors are ferric chloride, low molecular weight complexes of iron,such as poly functionality and complexes with carboxylic, ketone andhydroxyl functionality, such as acetylacetonate complexes of iron.

An additional component powder, such as a dopant-forming powder, can becombined with the iron oxide precursor powder. Particularly preferredinteracting-forming powders are compounds of nickel, zinc, manganese,yttrium, the rare earths, barium, calcium and silica. Further, anadditional component, such as an interacting component, for example achloride hydrate and/or nitrate hydrate and/or a 2, 5 complex can beincorporated into the coating during the maintaining step, for examplezinc acetylacetonate gas as a source of the metal interacting compound,preferably in a hydrogen chloride atmosphere. A combination of the twomethods can also be used for additional component incorporation,

The powder iron oxide precursor on melting is maintained and/orequilibrated as set forth above. In addition, temperatures can beadjusted and/or a component introduced into the melting/maintaining stepwhich can aid in altering the precursor for enhanced conversion to ironoxide. For example, gaseous hydrogen chloride can be introduced to formpartial or total halide salts and/or the temperature can be adjusted toenhance decomposition of, for example, iron or interacting organic saltsand/or complexes to more readily oxidizable iron compounds. Theinteracting compound can also be present in an oxide or precursor formin the melt as a dispersed preferably as a finely dispersed solid. Theoxide can be incorporated advantageously as part of the powder coatingof the substrate material.

A fluidizable coated substrate, such as substrates coated directly in afluid bed of powder, can be subjected to conditions which allow liquidusformation by the iron oxide precursor and coating of the substrate. Aparticularly preferred process uses a film forming amount of the ironoxide precursor which allows for coating during the liquidus step of theprocess, and which substantially reduces detrimental substrateagglomeration. The conditions are adjusted or controlled to allowsubstantially free substrate fluidization and transport under theconditions of temperature and bed density, such as dense bed density tolean bed density. The coated substrate can be further transported to theoxidation step for conversion to iron oxide or converted directly toiron oxide in the same reactor/processing system. A particularlypreferred embodiment is the transport of the liquidus coated substrateas a dense bed to a fluidized oxidation zone, such zone being afluidized zone preferably producing a conversion to iron oxide on thesubstrate of at least about 80% by weight.

The iron chloride precursor and/or interacting-forming component to becontacted with the substrate may be present in a molten state. Forexample, a melt containing molten iron chloride precursor and/orinteracting metal compound may be used. The molten composition mayinclude one or more other materials, having properties as noted above,to produce a mixture, e.g., a eutectic mixture, having a reduced meltingpoint and/or boiling point. The use of molten iron chloride precursorand/or interacting-forming component provides advantageous substratecoating while reducing the handling and disposal problems caused by asolvent. In addition, the substrate is very effectively and efficientlycoated so that coating material losses are reduced.

The iron chloride precursor and/or interacting-forming component to becontacted with the substrate may be present in a vaporous state. As usedin this context, the term "vaporous state" refers to both asubstantially gaseous state and a state in which the iron chlorideprecursor and/or interacting-forming component are present as drops ordroplets and/or mist in a carrier gas, i.e., an atomized state. Liquidstate iron chloride precursor and/or interacting-forming component maybe utilized to generate such "vaporous state" compositions.

In addition to the other materials, as noted above, the compositioncontaining iron chloride precursor and/or the interacting-formingcomponent may also include one or more grain growth inhibitorcomponents. Such inhibitor component or components are present in anamount effective to inhibit grain growth in the iron oxide-containingcoating. Of course, such grain growth inhibitor components should haveno substantial detrimental effect on the final product.

The interacting-forming component may be deposited on the substrateseparately from the iron chloride precursor, e.g., before and/or duringand/or after the iron chloride precursor/substrate contacting. If theinteracting-forming component is deposited on the substrate separatelyfrom the iron chloride precursor, it is preferred that theinteracting-forming component, for example, the nickel, manganese orzinc component, be deposited after the iron chloride precursor, such asto form soluble and/or eutectic mixtures and/or dispersion.

Any suitable interacting-forming component may be employed in thepresent process. Such interacting-forming component should providesufficient concentration so that the final iron oxide coating has thedesired properties, e.g., magnetic, high permeability, stability, etc.Care should be exercised in choosing the interacting-forming componentor components for use. For example, the interacting-forming componentshould be sufficiently compatible with the iron chloride precursor sothat the desired doped iron oxide coating can be formed.Interacting-forming components which have excessively high boilingpoints and/or are excessively volatile (relative to the iron precursor),at the conditions employed in the present process, are not preferredsince, for example, the final coating may not have optimum propertiesand/or a relatively large amount of the interacting-forming component orcomponents may be lost during processing. It may be useful to includeone or more property altering components, e.g., boiling pointdepressants, in the composition containing the interacting-formingcomponent to be contacted with the substrate. Such property alteringcomponent or components are included in an amount effective to alter oneor more properties, e.g., boiling point, of the interacting-formingcomponent, e.g., to improve the compatibility or reduce theincompatibility between the dopant-forming component and iron chlorideprecursor. Preferred dopant oxide precursors are set for above andinclude the halide, preferably the chlorides, organic complexes, such aslow molecular poly functional organic acids, complexes, preferably 2, 5,alkoxides, benzylates and the like. The preferred interacting componentsare those that provide for optimum interacting component incorporationwhile minimizing interacting precursor losses, particularly under thepreferred process condition as set forth herein. Oxides or suboxides canalso be used where interacting component incorporation is accomplishedduring the oxidation sintering contacting step.

The use of a interacting component is an important feature of certainaspects of the present invention. First, it has been found thatinteracting component can be effectively and efficiently incorporatedinto the iron oxide-containing coating. In addition, such interactingcomponents act to provide iron oxide-containing coatings with goodmagnetic properties referred to above, morphology and stability.

The liquid, e.g., molten, composition which includes iron chlorideprecursor may, and preferably does, also include the interacting-formingcomponent. In this embodiment, the interacting-forming component orcomponents are preferably soluble and/or dispersed homogeneously in thecomposition. Vaporous mixtures of interacting compounds and iron oxideforming components may also be used. Such compositions are effectivesince the amount of interacting components in the final iron oxidecoating can be controlled by controlling the make-up of the composition.In addition, both the iron chloride precursor and interacting-formingcomponent are deposited on the substrate in one step. Moreover, ifchlorides or organic precursors are used, such precursor components areconverted to oxides during the oxidizing agent/substrate contactingstep. This enhances the overall utilization of the coating components inthe present process.

In one embodiment, a vaporous iron chloride precursor composition isutilized to contact the substrate, and the composition is at a highertemperature than is the substrate. The make-up of the vaporous ironchloride-precursor containing composition is such that iron chlorideprecursor condensation occurs on the cooler substrate. If theinteracting-forming component is present in the composition, it ispreferred that such interacting-forming component also condense on thesubstrate. The amount of condensation can be controlled by controllingthe chemical make-up of the vaporous composition and the temperaturedifferential between the composition and the substrate. This"condensation" approach very effectively coats the substrate to thedesired coating thickness without requiring that the substrate besubjected to numerous individual or separate contactings with thevaporous iron chloride-precursor containing composition.

The substrate including the iron chloride-precursor containing coatingand the interacting-forming component-containing coating is contactedwith an oxidizing agent at conditions effective to convert iron chlorideprecursor to iron oxide, and form an iron oxide coating on at least aportion of the substrate. Water, e.g., in the form of a controlledamount of humidity, can be present provided that substantial deleteriouschanges in final iron oxide properties are controlled and/or minimizedduring the coated substrate/oxidizing agent contacting.

Any suitable oxidizing agent may be employed, provided that such agentfunctions as described herein. Preferably, the oxidizing agent (ormixtures of such agents) is substantially gaseous at the coatedsubstrate/oxidizing agent contacting conditions. The oxidizing agentpreferably includes reducible oxygen, i.e., oxygen which is reduced inoxidation state as a result of the coated substrate/oxidizing agentcontacting. More preferably, the oxidizing agent comprises molecularoxygen, either alone or as a component of a gaseous mixture, e.g., air.

The substrate may be composed of any suitable material and may be in anysuitable form. Preferably, the substrate is such so as to minimize orsubstantially eliminate the migration of ions and other species, if any,from the substrate to the iron oxide-containing coating which aredeleterious to the functioning or performance of the coated substrate ina particular application. In addition, it can be precoated to minimizemigration, for example an alumina and/or silica precoat and/or toimprove wetability and uniform distribution of the coating materials onthe substrate. Further, the iron oxide component, article can be furthercoated with a barrier film, organic and/or inorganic to minimizereaction of components such as corrosive gaseous components with thefinal iron oxide component/article. In order to provide for controlledmagnetic properties in the interacting iron oxide coating, it ispreferred that the substrate be substantially non-magnetic conductivewhen the coated substrate is to be used as a component of magnetic typedevices. In one embodiment, the substrate is inorganic, for examplemetal and/or ceramic and/or glass. Although the present process may beemployed to coat two dimensional substrates, such as substantially flatsurfaces, it has particular applicability in coating three dimensionalsubstrates. Thus, the present process provides substantial processadvances as a three dimensional process. Examples of three dimensionalsubstrates which can be coated using the present process include spheressuch as having a diameter of from about 1 micron to about 500 micronsmore preferably from about 10 microns to about 150 microns, extrudates,flakes, single fibers, fiber rovings, chopped fibers, fiber mats, poroussubstrates, irregularly shaped particles, e.g., catalyst supports,multi-channel monoliths, tubes and the like. The substrate for use inpolymer composites can be in the form of a particle type shapes setforth above and/or a body of woven or non-woven fibers, particularly, abody of woven or non-woven fibers having a porosity in the range ofabout 60% to about 95%. Porosity is defined as the percent or fractionof void space within a body of fibers. The above-noted porosities arecalculated based on the fibers including the desired oxide coating.

The conditions at which each of the steps of the present process occurare effective to obtain the desired result from each such step and toprovide a substrate coated with an iron oxide-containing coating. Thesubstrate/iron chloride precursor contacting and thesubstrate/interacting forming component contacting preferably occur at atemperature in the range of about 30° C. to about 450° C., morepreferably about 35° C. to about 300° C. The amount of time during whichiron chloride precursor and/or interacting-forming component is beingdeposited on the substrate depends on a number of factors, for example,the desired thickness of the iron oxide-containing coating, the amountsof iron chloride precursor and interacting-forming component availablefor substrate contacting, the method by which the iron chloride anddopant-forming component are contacted with the substrate and the like.Such amount of time is preferably in the range of about 0.1 or 0.5minutes to about 20 minutes, more preferably about 0.5 or 1 minute toabout 10 minutes.

If the coated substrate is maintained in a substantially non-deleteriousoxidizing environment, it is preferred that such maintaining occur at atemperature in the range of about 50° C. to about 450° C., morepreferably about 100° C. to about 300° C. for a period of time in therange of about 0.05 or 0.1 minutes to about 20 minutes, more preferablyabout 0.5 or 1 minute to about 10 minutes. The coatedsubstrate/oxidizing agent contacting preferably occurs at a temperaturein the range of about 60° C. to about 1000° C., more preferably about750° C. to about 900° C., for a period of time in the range of about0.05 or 0.1 minutes to about 10 minutes. Additional contacting at ahigher temperature up to about 850° C. for a period of up to about 0.5to about 2 hours can be used to fully develop the electricalconductivity properties. A particular advantage of the process of thisinvention is that the temperatures used for oxidation have been found tobe lower, in certain cases, significantly lower, i.e., 50° to 200° C.than the temperatures required for conventional processing. This is verysignificant and unexpected, provides for process efficiencies andreduces, and in some cases substantially eliminates, migration ofdeleterious elements from the substrate to the iron oxide layer.Excessive ion migration, e.g., from the substrate, can reducepermeability depending on the substrate and processing condition. Inaddition, the oxidizing and or sintering steps can be staged withsuccessive reductions in the oxygen content of the gas and/or with acarbon source, to provide the desired oxygen content for developingenhanced magnetic properties.

The pressure existing or maintained during each of these steps may beindependently selected from elevated pressures (relative to atmosphericpressure), atmospheric pressure, and reduced pressures (relative toatmospheric pressure). Slightly reduced pressures, e.g., less thanatmospheric pressure and greater than about 8 psia and especiallygreater than about 11 psia, are preferred.

Ferrite is a generic term describing a class of magnetic oxide compoundsthat contain iron oxide as a major component. There are several crystalstructure classes of compounds broadly defined as ferrites, such asspinel, magnetoplumbite, garnet, and perovskite structures.

Although there are many characterizations specific to a givenapplication, one property is shared by all materials designated asferrites, namely the existence of a spontaneous magnetization (amagnetic induction in the absence of an external magnetic field).

The magnetic properties of ferrites derive directly from the electronconfiguration of the ions and their interactions with each other.Although the specific structures differ, they can all generally beconsidered to be composed of two sublattices: a rigid anion latticecomposed of the relatively large oxygen anions and the cation sublatticeformed by the filling of holes (interstitial sites) with the smallercations.

Spinel ferrites has the general composition AB₂ X₄. The structure is acubic close packing of the Anions (X), with a variety of A and B cationscapable of filling the interstitial sites. The smallest crystallographicunit cell which has the required cubic symmetry contains eight formulaunits of AB₂ X₄. each unit cell has two types of interstitial sites thatcan be occupied by the A and B cations.

A wide variety of transition metal cations can fit into theseinterstitial sites. Thus it becomes possible to make a large number ofspinel ferrite compounds, each having specific magnetic interactions.

A great variety of oxide materials form the spinel structure withnickel-zinc-ferrite, Ni_(1-x) Zn_(x) Fe₂₋₅ O₄, andmanganese-zinc-ferrite, Mn_(1-x) Zn_(x) Fe₂₊₅ O₄, being preferred.

Many of the nickel-zinc-ferrites are formulated with an iron deficiencyin order to keep the magnetic losses low and the resistivity high (>10⁶·cm): The manganese-zinc-ferrites, on the other hand, have a slightexcess of iron in order to optimize permeability and magneticsaturation.

It is preferred to make cubic spinel ferrite materials which have thehighest inductance (high relative permeability) and are relatively easyto magnetize and demagnetize as high frequencies. These materials areused as inductors and high frequency transformers. Materials with thehighest permeability are those for which the anisotropy constant K₁ isapproximately zero and the compositional regions where K₁ is very lowhave been delineated.

In addition to the major crystal chemical interactions, a number ofdopants have specific effects on the magnetic properties of spinelferrites. For example, the addition of small amounts of CaO (0.1 mol %)and SiO₂ (0.02 mol %) greatly reduce the eddy current losses inferrites. Silica effects density, power losses, and microstructure ofmanganese-zinc-ferrites. Other dopants such as B₂ O₃, ZnO₂ and TiO₂ haveeffects on the temperature coefficient of permeability and permeabilitydisaccommodation.

In addition to the above spinel ferrited hexagonal ferrites are a groupof ferromagnetic oxides in which the principal component is Fe₂ O₃ incombination with a divalent oxide (BaO, SrO, or PbO) and a divalenttransition metal oxide (e.g., BaZn₂ Fe₁₆ O₂₇. Most hexagonal ferritematerials are used as permanent magnet materials.

In contrast to the spinel ferrites, where the object is to produce amaterial with the lowest possible value of the magnetocrystallineanisotropy (typically o-10₋₁₁ J/cm₃ at room temperature) in order tomaximize permeability and reduce hysteresis losses, the M-type hexagonalferrits are useful because of their high anisotropic value (typically3×10₋₁ J/cm₃).

The garnets represent another class of compounds having the generalstructure M₃ Fe₅ O₁₂. The unit cell within the structure there are 24tetrahedral and 16 octahedral sites. These sites can accommodate thesmall Fe cation and other cations of similar size. Additionally, thereare 24 dodecahedral sites that can accommodate Y, La,Ca, the rareearths, and other large cations.

Again, as was the case with both the hexagonal and spinel ferrites,there are two magnetic sublattice opposed to each other. The widevariety of cations that can be substituted into the lattice allowspecific material properties to be engineered. The most widely knowmagnetic compounds having this structure are yttrium-iron=garnet, Y₃ Fe₅O₁₂ (25), and gadolinium-iron-garnet, Gd₃ Fe₅ O₁₂.

The iron oxide coated substrate, of the present invention may be, forexample a magnetic material itself, a catalyst itself or a component ofa composite together with one or more matrix materials. The compositesmay be such that the matrix material or materials substantially totallyencapsulate or surround the coated substrate, or a portion of the coatedsubstrate may extend away from the matrix material or materials.

Any suitable matrix material or materials may be used in a compositewith the iron oxide coated substrate. Preferably, the matrix materialcomprises a polymeric material, e.g., one or more synthetic polymers,more preferably an organic polymeric material. The polymeric materialmay be either a thermoplastic material or a thermoset material. Amongthe thermoplastics useful in the present invention are the polyolefins,such as polyethylene, polypropylene, polymethylpentene and mixturesthereof; and poly vinyl polymers, such as polystyrene, polyvinylidene,combinations of polyphenylene oxide and polystyrene, and mixturesthereof. Among the thermoset polymers useful in the present inventionare epoxies, phenol-formaldehyde polymers, polyesters, polyvinyl esters,polyurethanes, melamine-formaldehyde polymers, and urea-formaldehydepolymers.

In order to provide enhanced bonding between the iron oxide coatedsubstrate and the matrix material, it has been found that the preferredmatrix materials have an increased polarity, as indicated by anincreased dipole moment, relative to the polarity of polypropylene.Because of weight and strength considerations, if the matrix material isto be a thermoplastic polymer, it is preferred that the matrix be apolypropylene-based polymer which includes one or more groups effectiveto increase the polarity of the polymer relative to polypropylene.Additive or additional monomers, such as maleic anhydride, vinylacetate, acrylic acid, and the like and mixtures thereof, may beincluded prior to propylene polymerization to give the productpropylene-based polymer increased polarity. Hydroxyl groups may also beincluded in a limited amount, using conventional techniques, to increasethe polarity of the final propylene-based polymer.

Thermoset polymers which have increased polarity relative topolypropylene are more preferred for use as the present matrix material.Particularly preferred thermoset polymers include epoxies,phenol-formaldehyde polymers, polyesters, and polyvinyl esters.

Various techniques, such as casting, molding and the like, may be usedto at least partially encapsulate or embed the iron oxide coatedsubstrate into the matrix material or materials and form composites. Thechoice of technique may depend, for example, on the type of matrixmaterial used, the type and form of the substrate used and the specificapplication involved. One particular embodiment involvespre-impregnating (or combining) that portion of the iron oxide coatedsubstrate to be embedded in the matrix material with a relatively polar(increased polarity relative to polypropylene) thermoplastic polymer,such as polar engineering thermoplastic resins, prior to the coatedsubstrate being embedded in the matrix material. This embodiment isparticularly useful when the matrix material is itself a thermoplasticpolymer, such as modified polypropylene, and has been found to provideimproved bonding between the iron oxide coated substrate and the matrixmaterial.

The bonding between the matrix material and the iron oxide coatedsubstrate is important. In order to provide for improved bonding of theiron oxide coating (on the substrate) with the matrix material, it ispreferred to at least partially, more preferably substantially totally,coat the iron oxide coated substrate with a coupling agent which acts toimprove the bonding of the iron oxide coating with the matrix. This isparticularly useful when the substrate is a ceramic comprises acidresistant glass fibers. Any suitable coupling agent may be employed.Such agents preferably comprise molecules which have both a polarportion and a non-polar portion. Certain materials generally in use assizing for glass fibers may be used here as a "size" for the iron oxidecoated glass fibers. The amount of coupling agent used to coat the ironoxide coated ceramic fibers should be effective to provide the improvedbonding noted above and, preferably, is substantially the same as isused to size bare glass fibers. Preferably, the coupling agent isselected from the group consisting of silanes, silane derivatives,stannates, stannate derivatives, titanates, titanate derivatives andmixtures thereof. As set forth below, such composites are particularlyuseful in antistatic type applications for example, in staticdissipation and electro static recording.

In yet another embodiment, a coated substrate including iron oxide,preferably high permeability iron oxide, and at least one additionalcatalyst component in an amount effective to promote a chemical reactionis formed. Preferably, the additional catalyst component is a metaland/or a component of a metal effective to promote the chemicalreaction. The promoting effect of the catalyst component may be enhancedby the presence of a magnetic field in proximity to the componentincluding induction heating of the catalyst. Thus, the iron oxide,preferably on a substantially non-electronically conductive substrate,e.g., a catalyst support, can provide an effective and efficientcatalyst for chemical reactions, including those which occur or areenhanced when a magnetic field is applied in proximity to the catalystcomponent. Thus, it has been found that the present coated substratesare useful as active catalysts and supports for additional catalyticcomponents. Without wishing to limit the invention to any particulartheory of operation, it is believed that the outstanding stability,e.g., with respect to properties and/or morphology and/or stability, ofthe present iron oxides plays an important role in making useful andeffective catalyst materials particularly the higher surface areaattainable of copper oxide materials prepared in accordance with thisinvention, especially when compared to prior art sintering processes.Any chemical reaction, including a chemical reaction the rate of whichis magnetic field or enhanced as described herein, may be promoted usingthe present catalyst component iron oxide-containing coated substrates.A particularly useful class of chemical reactions are those involvingchemical oxidation or reduction. For example, chemical reactions, e.g.,dehydrogenation, such as alcohols to ketones, hydrodecyclization,isomerization, ammoxidation, such as with olefins, aldol condensationsusing aldehydes and carboxylic acids and the like, may be promoted usingthe present catalyst component, iron oxide-containing coated substrates.As noted above, the iron oxide in the catalyst component, ironoxide-containing substrates is magnetic. Although magnetic iron oxideitself is particularly useful, other interacting components may beincorporated in the present catalyst materials to provide the iron oxidewith the desired magnetic properties. Such interacting components may beincorporated into the final catalyst component, iron oxide-containingcoated substrates using one or more processing techniques substantiallyanalogous to procedures useful to incorporate such interactingcomponents, e.g., as described herein.

Particularly useful chemical reactions as set forth above include theoxidative dehydrogenation of ethylbenzene to styrene and 1-butene to1,3-butadiene; the ammoxidation of propylene to acrylonitrile; aldolcondensation reactions for the production of unsaturated acids, i.e.,formaldehyde and propionic acid to form methacrylic acid andformaldehyde and acetic acid to form acrylic acids; the isomerization ofbutenes; and the oxidation of methane to methanol.

The iron oxide-containing coated substrates of the present invention maybe employed alone or as a catalyst and/or support in a sensor, inparticular gas sensors. Preferably, the coated substrates includes asensing component similar to the catalyst component, as describedherein. The present sensors are useful to sense the presence orconcentration of a component, e.g., a gaseous component, of interest ina medium, for example, hydrogen, carbon monoxide, methane and otheralkanes, alcohols, aromatics, e.g., benzene, etc., e.g., by providing asignal in response to the presence or concentration of a component ofinterest, e.g., a gas of interest, in a medium. Such sensors are alsouseful where the signal provided is enhanced by the presence of anelectrical field or current in proximity to the sensing component. Thesensing component is preferably one or more metals or metalliccontaining sensing components, for example, platinum, palladium, silverand iron. The signal provided may be the result of the component ofinterest itself impacting the sensing component and/or it may be theresult of the component of interest being chemically reacted, e.g.,oxidized or reduced, in the presence of the sensing component.

The stability and durability for the present particularly useful ironoxide materials are believed to make them very useful as catalysts,sensors.

Any suitable catalyst component (or sensing component) may be employed,provided that it functions as described herein. Among the useful metalcatalytic components and metal sensing components are those selectedfrom components of the transition metals, the rare earth metals, certainother catalytic components and mixtures thereof, in particular catalystscontaining gold, silver, copper, vanadium, chromium, tungsten, iron,indium, antimony, the platinum group metals, i.e., platinum, palladium,iron, nickel, manganese, cesium, titanium, etc. Although metalcontaining compounds may be employed, it is preferred that the metalcatalyst component (and/or metal sensing component) included with thecoated substrate comprise elemental metal and/or metal in one or moreactive oxidized forms, for example, Cr₂ O₃, Ag₂ O, Sb₂ O₄, etc.

The preferred support materials include a wide variety of materials usedto support catalytic species, particularly porous refractory inorganicoxides. These supports include, for example, alumina, silica, zirconia,magnesia, boria, phosphate, titania, ceria, thoria and the like, as wellas multi-oxide type supports such as alumina-phosphorous oxide, silicaalumina, zeolite modified inorganic oxides, e.g., silica alumina, andthe like. As set forth above, support materials can be in many forms andshapes, especially porous shapes which are not flat surfaces, i.e., nonline-of-site materials. A particularly useful catalyst support is amulti-channel monoliths such as one made from corderite which has beencoated with alumina. The catalyst materials can be used as is or furtherprocessed such as by sintering of powdered catalyst materials intolarger aggregates. The aggregates can incorporate other powders, forexample, other oxides, to form the aggregates.

The catalyst components (or sensing components) may be included with thecoated substrate using any one or more of various techniques, e.g.,conventional and well known techniques. For example, metal catalystcomponents (metal sensing components) can be included with the coatedsubstrate by impregnation; electrochemical deposition; spray hydrolysis;deposition from a molten salt mixture; thermal decomposition of a metalcompound or the like. The amount of catalyst component (or sensingcomponent) included is sufficient to perform the desired catalytic (orsensing function), respectively, and varies from application toapplication. In one embodiment, the catalyst component (or sensingcomponent) is incorporated while the iron oxide forming component isplaced on the substrate. Thus, a catalyst material, such as a salt oracid, e.g., a halide and preferably chloride, oxy chloride and chloroacids, e.g., chloro platinic acid, of the catalytic metal, isincorporated into the iron chloride-precursor containing coating of thesubstrate, prior to contact with the oxidizing agent, as describedherein. This catalyst material can be combined with the ironchloride-precursor and contacted with the substrate, or it may becontacted with the substrate separately from iron chloride-precursorbefore, during and/or after the iron chloride-precursor/substratecontacting.

The preferred approach is to incorporate catalyst-forming materials intoa process step used to form a iron oxide coating. This minimizes thenumber of process steps but also, in certain cases, produces moreeffective catalysts. The choice of approach is dependent on a number offactors, including the process compatibility of iron oxide andcatalyst-forming materials under given process conditions and theoverall process efficiency and catalyst effectiveness.

A particularly unique property of the catalysts of this invention is theability to be able to separate and recover catalyst from solution and/orother non-magnetic or low permeability solids by magnetic separation.This is particularly advantageous in slurry catalysts, such as in liquidsystems, such as hydrocarbon and/or aqueous and/or combination systems.This property allows separation including separation from othernon-magnetic solids and separate catalysts regeneration if required.

Another unique property is the ability to heat the catalyst by inductionheating as more fully described below. This property allows for farsuperior temperature control and thermal efficiencies.

In addition, the ability to vary coating thickness and substratecomposition allows designing catalyst for a given density, a featureimportant in gravity separation processes.

The iron oxide/substrate combinations, e.g., the iron oxide coatedsubstrates, of the present invention are useful in other applications aswell.

The applications for the spinel ferrites can be grouped into severalmain categories: main cores, and linear, power, and recording-headapplications.

Magnetic-core memories are based on switching small toroidal cores ofspinel ferrite between two stable magnetic states. Such core memoriesare used in applications where ruggedness and reliability are necessary,e.g., military applications.

The linear or low signal applications are those in which the magneticfield in the ferrite is well below the saturation level and the relativemagnetic permeability can be considered constant over the operatingconditions.

The manganese-zinc-ferrite materials characteristically have higherrelative permeabilities, higher saturation magnetization, lower losses,and lower resistivities. Since the ferromagnetic resonance frequency isdirectly related to the permeability, the usual area of application isbelow 2 MHz.

At low signal levels, ferrite cores are used as transformers, lowfrequency and pulse transformers, or low energy inductors. As inductors,the manganese-zinc-ferrites find numerous applications in the design oftelecommunications equipment where they must provide a specificinductance over specific frequency and temperature ranges.Nickel-zinc-ferrites with lower saturation magnetization, generallylower relative magnetic permeabilities, and lower resistivities (10⁶·cm), produce ferromagnetic resonance effects at much higher frequenciesthan the manganese-zinc-ferrites. They find particular application atfrequencies from 2 to 70 MHz (46).

By adjustment of the nickel-zinc ratio it is possible to prepare aseries of materials covering the relative permeability range of 10-2000.These materials are used as high frequency inductors, antenna rods, highfrequency power transformers, and pulse transformers. A variety ofmaterials have been developed to serve these applications.

The lower magnetic losses of ferrite materials and its higher resistance(10 ohm·cm) compared with laminated transformer steel permits ferritecores to be used as the transformer element in high frequency powersupplies. Commonly known as switched-mode power supplies, they operateat a frequency of 15-30 kHz and offer higher efficiencies and smallersize than comparable laminated steel transformers.

Television and audio applications include yoke rings for the deflectioncoils for television picture tubes, flyback transformers, and variousconvergence and pincushion distortion corrections as well as antennarods.

Manganese-zinc and nickel-zinc-spinel ferrites are used in magneticrecording heads for duplicating magnetic tapes and the recording ofdigital information. Most recording heads are fabricated frompolycrystalline nickel-zinc-ferrite for operating frequencies of 100 kHzto 2.5 GHz.

The unique properties of hexagonal ferrites are low density, and highcoercive force.

The ceramic magnet can be used in d-c permanent magnet motors,especially in automotive applications, such window life, flower, andwindshield-wiper motors.

Other grades of barium and strontium ferrite material have beendeveloped for similar applications.

Other applications of hexagonal ferrites are in loudspeakers. Hexagonalferrites are used in self-resonant isolators where the strongmagnetocrystalline anisotropy permits a resonator without large d-cmagnetic biasing fields.

Hexagonal ferrites are also used as magnetic biasing components inmagnetic bubble memories. porous membranes, resistance heating elements,electrostatic dissipation and recording elements, and electromagneticinterference shielding elements.

In one embodiment, a porous membrane is provided which comprises aporous substrate, preferably an inorganic substrate, and a ironoxide-containing material in contact with at least a portion of theporous substrate. In another embodiment, the porous membrane comprises aporous organic matrix material, e.g., a porous polymeric matrixmaterial, and a iron oxide-containing material in contact with at leasta portion of the porous organic matrix material. With the organic matrixmaterial, the iron oxide-containing material may be present in the formof an inorganic substrate, porous or substantially non porous, having airon oxide-containing coating, e.g., an magnetic iron oxide-containingcoating, thereon.

One particularly useful feature of the present porous membranes is theability to control the amount of iron oxide present to provide forenhanced performance in a specific application, e.g., a specificcontacting process. For example, the thickness of the ironoxide-containing coating can be controlled to provide such enhancedperformance. The coating process of the present invention isparticularly advantageous in providing such controlled coatingthickness. Also, the thickness of the iron oxide-containing coating canbe varied, e.g., over different areas of the same porous membrane, suchas an asymmetric porous membrane. In fact, the thickness of this coatingcan effect the size, e.g., diameter, of the pores. The size of the poresof the membrane or porous substrate may vary inversely with thethickness of the coating. The coating process of the present inventionis particularly useful in providing this porosity control.

A heating element, for example, an induction heating element, isprovided which comprises a three dimensional substrate having a magneticiron oxide-containing coating on at least a portion of all threedimensions thereof. The coated substrate is adapted and structured toprovide heat in response, that is, in direct or indirect response, tothe presence or application of one or more force fields, for example,magnetic fields, and the like, therein or thereto. An example of such aheating element is one which is adapted and structured to provide heatupon the application of a magnetic field. Heating elements which areadapted and structured to provide heat in response to the presence ofone or more magnetic fields therein are included in the scope of thepresent invention. In one embodiment, a flexible heating element isprovided which comprises a flexible matrix material, e.g., an organicpolymeric material as set forth above in contact with a substrate havingan magnetic iron oxide-containing coating on at least a portion thereof.The coated substrate is adapted and structured as described above.

In addition, an electrostatic dissipation/recording, electromagneticinterference shielding element is provided which comprises a threedimensional substrate, e.g., an inorganic substrate, having anelectronically conductive iron oxide-containing coating on at least aportion of all three dimensions thereof. The coated substrate is adaptedand structured to provide at least one of the following: electrostaticdissipation or recording and/or electromagnetic interference shielding.

A very useful application for the products of this invention is forstatic, for example, electrostatic, dissipation or recording andshielding, particularly for ceramic and polymeric parts, and moreparticularly as a means for effecting static dissipation includingcontrolled static charge and/or dissipation in such as parts made ofceramics and polymers and the like, as described herein. The presentproducts can be incorporated directly into the polymer or ceramic and/ora carrier such as a cured or uncured polymer based carrier or otherliquid, as for example in the form of a liquid, paste, hot melt, filmand the like. These product/carrier based materials can be directlyapplied to parts to be treated to improve overall performanceeffectiveness. A heating cycle is generally used to provide for productbonding to the parts. In addition, the products of this invention can beused in molding processes to allow for enhanced static dissipationand/or shielding properties of polymeric resins relative to an articleor device or part without such product or products, and/or to have apreferential distribution of the product or products at the surface ofthe part for greater volume effectiveness within the part.

The particular form of the products, i.e., fibers, flakes, particles,mats or the like, is chosen based upon the particular requirements ofthe part and its application, with one or more of flakes, fibers andparticles, including spheres, being preferred for polymeric parts. Ingeneral, it is preferred that the products of the invention have alargest dimension, for example, the length of fiber or particle or sideof a flake, of less than about 1/8 inch, more preferably less than about1/64 inch and still more preferably less than about 1/128 inch. It ispreferred that the ratio of the longest dimension, for example, length,side or diameter, to the shortest dimension of the products of thepresent invention be in the range of about 500 to 1 to about 10 to 1,more preferably about 250 to 1 to about 25 to 1. The concentration ofsuch product or products in the product/carrier and/or mix is preferablyless than about 60 weight %, more preferably less than about 40 weight%, and still more preferably less than about 20 weight %. A particularlyuseful concentration is that which provides the desired performancewhile minimizing the concentration of product in the final article,device or part.

The products of this invention find particular advantage in staticdissipation parts, for example, parts having a surface resistivity inthe range of about 10⁴ ohms/square to about 10¹² ohms/square. Inaddition, those parts generally requiring shielding to a surfaceresistivity in the range of about 1 ohm/square to about 10⁵ ohms/squareand higher find a significant advantage for the above products due totheir mechanical properties and overall improved polymer compatibility,for example, matrix bonding properties as compared to difficult to bondmetal and carbon-based materials.

A flexible electrostatic dissipation/recording/electromagneticinterference shielding element is also included in the scope of thepresent invention. This flexible element comprises a flexible matrixmaterial, e.g., an organic polymeric material, in contact with asubstrate having an electronically conductive iron oxide-containingcoating on at least a portion thereof. The coated substrate of thisflexible element is adapted and structured as described above.

The present coating process is particularly suitable for controlling thecomposition and structure of the coating on the substrate to enhance theperformance of the coated substrate in a given, specific application,e.g., a specific resistance heating electrostatic dissipation, recordingor electromagnetic interference shielding application.

The present iron oxide/substrate combinations and matrix material/ironoxide/substrate combinations, which have at least some degree ofporosity, hereinafter referred to as "porous contacting membranes" or"porous membranes", may be employed as active components and/or assupports for active components in systems in which the ironoxide/substrate, e.g., the iron oxide coated substrate, is contactedwith one or more other components such as in, for example, separationsystems, gas and particulate purification systems, filter mediumsystems, flocculent systems and other systems in which the magneticproperties stability and durability of such combinations can beadvantageously utilized.

Particular applications which combine many of the outstanding propertiesof the products of the present invention include porous and magneticmembrane separations for solids processing, liquids processing, gasprocessing, food processing, chemical processing, and bio medicalprocessing. For example, various types of solutions can be furtherconcentrated. The separation system can be used in flat plate, tubularand/or spiral wound system design.

Membranes containing voids that are large in comparison with moleculardimensions are considered porous. In these porous membranes, the poresare interconnected, and the membrane may comprise only a few percent ofthe total volume. Transport, whether driven by pressure, concentration,or electrical potential or magnetic field, occurs within these pores.Many of the transport characteristics of porous membranes are determinedby the pore structure, with selectivity being governed primarily by therelative size of the molecules or particles involved in a particularapplication compared to the membrane pores. Mechanical properties andchemical resistance are greatly affected by the nature, composition andstructure e.g., chemical composition and physical state, of themembrane.

Commercial micropore membranes have pore dimensions, e.g., diameters, inthe range of about 0.005 micron to about 20 microns. They are made froma wide variety of materials in order to provide a range of chemical andsolvent resistances. Some are fiber or fabric reinforced to obtain therequired mechanical rigidity and strength. The operationalcharacteristics of the membrane are defined sometimes in terms of themolecules or particles that will pass through the membrane porestructure.

Microporous membranes are often used as filters. Those with relativelylarge pores are used in separating coarse disperse, suspendedsubstances, such as particulate contamination. Membranes with smallerpores are used for sterile filtration of gases, separation of aerosols,and sterile filtration of pharmaceutical, biological, and heat sensitivesolutions. The very finest membranes may be used to separate, e.g.,purify, soluble macromolecular compounds.

Porous membranes also are used in dialysis applications such a removingwaste from human blood (hemodialysis), for separation of biopolymers,e.g., with molecular weights in the range of about 10,000 to about100,000, and for the analytical measurements of polymer molecularweights. Microporous membranes also may be used as supports for verythin, dense skins or a containers for liquid membranes.

The ability of dense membranes to transport species selectively makespossible molecular separation processes such as desalination of water orgas purification, but with normal thicknesses these rates are extremelyslow. In principle, the membranes could be made thin enough that therates would be attractive, but such thin membranes would be verydifficult to form and to handle, and they would have difficultysupporting the stresses imposed by the application. Conversely,microporous membranes have high transport rates but very poorselectivity for small molecules. Asymmetric membranes, for example madeof the present combinations, in which a very thin, dense membrane isplaced in series with a porous substructure are durable and provide highrates with high selectivity. Such asymmetric membranes and the usethereof are within the scope of the present invention.

Examples of applications for porous membranes include: separation offungal biomass in tertiary oil recovery; concentration of PVC latexdispersions; desalination of sea water; enhancement of catecholaminedetermination; removal of colloids from high purity deionized water;treatment of wool scouring liquids; filtration of tissue homogenates;separation of antigen from antigen-antibody couple in immunoassay;purification of subcutaneous tissue liquid extracts; concentration ofsolubilized proteins and other cellular products; cell debris removal;concentration of microbial suspensions (microbial harvesting); enzymerecovery; hemodialysis; removal of casein, fats and lactose from whey;concentration of albumen; separation of skimmed milk; clarification ofliqueur, fruit juices, sugar, and corn syrup; alcohol fermentation;sterilization of liquids, e.g., beer, wine; continuous microfiltrationof vinegar; concentration and demineralization of cheese, whey, soywhey, vegetable extracts, and flavorings; sugar waste recovery; silverrecovery from photo rinses; dewatering of hazardous wastes; removal ofhydrocarbon oils from waste water; recovery and recycling of sewageeffluent; recovery of dye stuffs from textile mill wastes; recovery ofstarch and proteins from factory waste, wood pulp, and paper processing;separation of water and oil emulsions; separation of carbon dioxide andmethane; and catalytic chemical reactions.

As described above porous membranes can be used in a wide variety ofcontacting systems. In a number of applications, the porous membraneprovides one or more process functions including: filtration,separation, purification, recovery of one or more components, emulsionbreaking, demisting, flocculation, resistance heating and chemicalreaction (catalytic or noncatalytic), e.g., pollutant destruction to anon-hazardous form. The resistance heating and chemical reactionfunctions (applications) set forth herein can be combined with one ormore other functions set forth herein for the porous membranes as wellas such other related porous membrane applications.

The porous membrane, in particular the substrate, can be predominatelyorganic or inorganic, with an inorganic substrate being suitable formore demanding process environments. Depending upon the application, theiron oxide film can be provided with a barrier coating on its surface tominimize and/or reduce substantial detrimental outside environmentaleffects and/or conditions on the iron oxide surface. The porousorganic-containing membranes often include a porous organic basedpolymer matrix material having incorporated therein a three dimensionaliron oxide-containing material, preferably including an magnetic irondioxide coating, more preferably incorporating a additional interactingcomponent and/or a catalytic species, in an amount that provides thedesired function, particularly high permeability, without substantiallydeleteriously affecting the properties of the organic polymer matrixmaterial. These modified polymer membranes are particularly useful inporous membrane and/or magnetic separation and/or magneticsusceptablematerial and/or catalytic processes.

Examples of polymer materials useful in microporous membranes includecellulose esters, poly(vinyl chloride), high temperature aromaticpolymers, polytetrafluoroethylene, polymers sold by E. I. DuPontCorporation under the trademark Nafion, polyethylene, polypropylene,polystyrene, polyethylene, polycarbonate, nylon, silicone rubber, andasymmetric coated polysulfone fiber.

A very convenient application for the coating process and products ofthis invention is the production of a controlled coating, e.g., a thincoating of iron oxide-containing material, on an inorganic substrate,particularly a porous inorganic substrate, to produce a porous membrane.The process provides a new generation of membranes: porous membranes forcontacting processes, e.g., as described herein. The selectivity infiltration, particularly ultra and micro filtration, can also beenhanced by applying an magnetic field with magnetic susceptiblematerial. The magnetic field can be obtained using a membrane includinga magnetic iron oxide-containing coated substrate.

Porous multilayer asymmetric electrically inorganic membranes, producedin accordance with this invention, are particularly advantageous formembrane applications. Among the advantages of such membranes are:stability at high temperature and/or at large pressure gradients,mechanical stability (reduced and even substantially no compaction ofthe membrane under pressure), stability against microbiological attack,chemical stability especially with organic solvents, steam sterilizationat high temperatures, backflush cleaning at pressures of up to 25 atm,and stability in corrosive and oxidation environment.

A membrane can be classified as a function of the size of the particles,macromolecules and molecules separated. Micron sized porous ceramics forfiltration processes can be prepared through sintering of appropriatematerials as set forth herein for the manufacture of sensors. However,the preferred process for membrane-based microfiltration,ultrafiltration and reverse osmosis is to provide inorganic layers withultrafine pores and thickness small enough to obtain high flux throughthe membrane, particularly membranes including iron oxide-containingcoatings.

With this type of asymmetric membrane, separation processes are pressuredriven. Another factor is the interaction at the membrane interfacebetween the porous material and the material to be processed. As notedabove, selectivity can be enhanced by applying an magnetic field ontothe surface of the membrane particularly with magnetic susceptiblematerials. Such porous membranes can be obtained with one or moremagnetic iron oxide-containing thin layers on a porous substrate.Conductive iron oxide combined with other metal oxide mixtures alsoprovide improved properties for porous membranes and can exhibitmagnetic and electronic conductivity, as well as other functions, suchas catalysis or resistance heating.

As set forth above, porous membranes with inorganic materials can beobtained through powder agglomeration, the pores being the intergranularspaces. Conflicting requirements such as high flow rate and mechanicalstability can be achieved using an asymmetric structure. Thus, aninorganic porous membrane is obtained by superimposing a thinmicroporous film, which has a separative function, over a thickmacroporous support. For example, conductive iron oxide coating onto thesurface of filter media can be used as well as onto the surface of flatcircular alumina plates. Coated alumina membranes supported on the innerpart of sintered alumina tubes designed for industrial ultrafiltrationprocesses can be used. Tube-shaped supports can be used with varyingdifferent chemical compositions, such as oxides, carbides, and clays.Coating of a homogeneous and microporous iron oxide-containing layerdepends on surface homogeneity of the support and on adherence betweenthe membrane and its support. Superior results can be obtained withparticulate alumina. The inner part of the tube has a membranecomprising a layer, e.g., in the range of about 10 to about 20 micronsthick, with pores, e.g., having diameters in the range of about 0.02 toabout 0.2 microns sized for microfiltration purposes. The main featureof such a membrane is uniform surface homogeneity allowing for the ironoxide-containing coating to be very thin, e.g., less than about onemicron in thickness.

The products of this invention, as described herein, are particularlyuseful for resistance heating applications. It has been found that thecoated three dimensional and/or flexible substrates particularly fibers,flakes, particles, including spheres, fiber rovings, chopped fibers, andfiber mats, can be incorporated into polymeric matrix materials,particularly thermoplastic, thermoset and rubber based polymericmaterials, as described herein. The iron oxide coated substrates can be,for example, E, C, S, or T glass, silica, silica alumina, silica aluminaboria, silicon carbide or alumina fibers, rovings, mats, chopped mats,etc. What is unexpected is the improved mechanical properties, e.g.,strength, coating adhesion and the like, of the coated substratesrelative to the prior art substrates coated using spray pyrolysistechniques and the improved control over coating thickness to matchmagnetic requirements for a given heating application. Whereas for manylow to moderate temperature applications, organic polymer matrixmaterials are preferred, three dimensional products comprising,preferably primarily comprising flexible or rigid inorganic substratescoated with iron oxide-containing coatings have excellent hightemperature performance characteristics useful, for example, in hightemperature induction heating of liquids and gases, such as air, bycontact with or through (i.e., porous) such three dimensional products,including multi-channel monoliths. Typical induction heatingapplications include: the curing and bonding of polymeric composites.

A very useful application for the products of this invention is for thejoining of parts, particularly polymeric parts, and as a means foreffecting the sintering or curing of parts, such as ceramics, curablepolymers, for example thermoset and rubber based polymers and the like.The products can be incorporated directly into the polymer or ceramicand/or a carrier such as a cured or uncured polymer based carrier orother liquid, as for example in the form of a liquid, paste, hot melt,film and the like. These product/carrier based materials can be directlyapplied to parts to be joined and induction heating particularlyinduction heating used to raise the temperature and bond the partstogether at a joint such as through polymer melting and/or curing. Aparticular unexpected advantage is the improved mechanical properties,especially compared to metallic susceptors which may compromisemechanical properties. In addition, the products of this invention canbe used in molding processes to preferentially allow the rapid heatingand curing of polymeric resins, and/or to have a preferentialdistribution of the products at the surface of the parts for subsequentjoining of parts. The particular form of the products, i.e., fibers,flakes, particles, mats or the like, is chosen based upon the particularrequirements of the part and its application, with one or more offlakes, fibers and particles being preferred for joining or bondingparts. In general, it is preferred that the products of the inventionhave a largest dimension, for example the length of a fiber or side of aflake, of less than about 1/8 inch, more preferably less than about 1/64inch and still more preferably less than about 1/128 inch. Theconcentration of such product or products in the product/carrier and/ormix is preferably less than about 50 weight %, more preferably less thanabout 20 weight %, and still more preferably less than about 10 weight%. A particularly useful concentration is that which provides thedesired heating while minimizing the concentration of product in thefinal part.

A particularly unique application that relies upon stable electronicconductivity and the physical durability of the products of thisinvention are dispersions of conductive material, such as powders, influids, e.g., hydrocarbons, e.g., mineral or synthetic oils, whereby anincrease in viscosity, to even solidification, is obtained when amagnetic field is applied to the system. These fluids are referred to as"field dependent" fluids which congeal and which can withstand forces ofshear, tension and compression. These fluids revert to a liquid statewhen the magnetic field is turned off. Applications include dampening,e.g., shock absorbers, particularly for heavy duty cycling applications.

Certain of these and other aspects the present invention are set forthin the following description of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block flow diagram illustrating a process for producing thepresent coated substrates.

FIG. 2 is a schematic illustration showing an embodiment of theresistance heating element of the present invention.

FIG. 3 is a detailed, somewhat schematic illustration of a portion ofthe resistance heating element shown in FIG. 2.

FIG. 4 is a blown-up, cross-sectional view of an individual coated fiberof the coated substrate shown in FIG. 3.

FIG. 5 is a detailed, somewhat schematic illustration of an alternateembodiment of the resistance heating element of the present invention.

FIG. 6 is a detailed, somewhat schematic illustration of a furtherembodiment of the heating element of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description specifically involves the coating of randomlyoriented, non-woven mats of alumina silica fibers. However, it should benoted that substantially the same process steps can be used to coatother substrate forms and/or materials, such as ceramic fibers and mats.

A process system according to the present invention, shown generally at10, includes a preheat section 12, a coating section 14, anequilibration section 16 and an oxidation/sintering section 18. Each ofthese sections is in fluid communication with the others. Preferably,each of these sections is a separate processing zone or section.

First gas curtain 20 and second gas curtain 22 provide inert gas,preferably nitrogen, at the points indicated, and, thereby effectivelyinsure that preheat section 12, coating section 14 and equilibriumsection 16 are maintained in a substantially inert environment and/or asubstantial non-deleterious oxygen environment. First exhaust 24 andsecond exhaust 26 are provided to allow vapors to exit or be vented fromprocess system 10.

Randomly oriented non-woven mats of silica alumina fibers from substratesource 28 are fed to preheat section 12 where the mats are preheated upto a maximum of 375° C. for a time of 1 to 3 minutes at atmosphericpressure to reach thermal equilibrium. These mats are composed of from 5micron to about 35 micron diameter silica alumina randomly oriented orwoven fibers. The mats are up to 42 inches wide and between 0.058 to0.174 mil thick. The mats are fed to process system 10 at the rate ofabout 1 to 5 feet per minute so that the fiber weight throughout isabout 0.141 to about 2.1 pounds per minute.

The preheated mats pass to the coating section 14 where the mats arecontacted with an anhydrous mixture from raw material source 30. Thiscontacting effects a coating of this mixture on the mats.

This contacting may occur in a number of different ways. For example,the ferric chloride hexahydrate can be combined with nitrogen to form avapor which is at a temperature of from about 25° C. to about 150° C.higher than the temperature of the mats in the coating section 14. Asthis vapor is brought into contact with the mats, the temperaturedifferential between the mats and the vapor and the amount of themixture in the vapor are such as to cause controlled amounts of ferricchloride hexahydrate to condense on and coat the mats.

Another approach is to apply the ferric chloride and interactingcompound for example manganese dichloride tetra hydrate and zincchloride (liquid and/or colloidal suspension of particles) in a moltenform directly to the mats in an inert atmosphere. There are severalalternatives for continuously applying the molten mixture to the mats.Obtaining substantially uniform distribution of the mixture on the matsis a key objective. For example, the mats can be compressed between tworollers that are continuously coated with the molten mixture. Anotheroption is to spray the molten mixture onto the mats. The fiber mats mayalso be dipped directly into the melt. The dipped fiber mats may besubjected to a compression roller step, a vertical lift step and/or avacuum filtration step to remove excess molten mixture from the fibermats.

An additional alternative is to apply the FeCl₃ or mixture in an organicsolvent. The solvent is then evaporated, leaving a substantially uniformcoating on the fiber mats. The solvent needs to be substantiallynon-reactive (at the conditions of the present process) and provide forsubstantial solubility of FeCl₃. For example, the dipping solutioninvolved should preferably be at least about 0.1 molar in FeCl₃.Substantially anhydrous solvents comprising benzene, acetonitrile, ethylacetate, acetone, propylene carbonate and mixtures thereof are suitable.Although the interacting compound may be introduced in the sinteringsection 18, it is preferred to incorporate the interacting compound inthe coating section 14 or the equilibration section 16, more preferablythe coating section 14.

Any part of process system 10 that is exposed to FeCl₃ or itshexahydrate melt or vapor is preferably corrosion resistant, morepreferably lined with inert refractory material.

In any event, the mats in the coating section 14 are at a temperature ofup to about 450° C., preferable up to about 300° C. and this section canbe operated at slightly less than atmospheric pressure. If the FeCl₃coating is applied as a molten melt in a solvent between compressionrollers, it is preferred that such compression rollers remain in contactwith the fiber mats for about 0.1 to about 2 minutes, more preferablyabout 1 to about 2 minutes.

After the iron chloride precursor coating is applied to the fiber mats,the fiber mats are passed to the equilibration section 16. Here, thecoated fiber mats are maintained, preferably at a higher temperaturethan in coating section 14, in a substantially inert and/ornon-deleterious oxygen environment atmosphere for a period of time,preferably up to about 10 minutes, to allow the coating to moreuniformly distribute over the fibers. In addition, if the interactingcomponent is introduced onto the fiber mats separate from the ferricchloride or its hydrate, the time the coated fiber mats spend in theequilibration section 16 results in such component becoming moreuniformly dispersed or distributed throughout the ferric chloridecoating. Further, it is preferred that any vapor and/or liquid whichseparate from the coated fiber mats if any in the equilibration section16 be transferred back and used in the coating section 14. Thispreferred option, illustrated schematically in FIG. 1 by lines 32 (forthe vapor) and 34 (for the liquid) increases the effective overallutilization of ferric chloride precursor in the process so that lossesof these components, as well as other materials such as solvents, arereduced.

The coated fiber mats are passed from the equilibration zone 16 into thesintering zone 18 where such fiber mats are contacted with an oxidizer,such as an oxygen-containing gas, from line 36. The oxidizer preferablycomprises a mixture of air and rate accelerating quantities of watervapor, if necessary. This mixture is contacted with the coated fibermats at atmospheric pressure at a temperature of about 600° C. to about1000° C. for up to about 10 minutes, optionally followed by atemperature up to about 850° C.-optionally in the presence of stageddilute oxygen and/or a carbon and/or source. Such contacting results inconverting the coating on the fiber mats to a magnetic iron dioxidecoating. The magnetic iron oxide coated fiber mats product, which exitssintering section 18 via line 38, has useful magnetic properties. Thisproduct preferably has an iron oxide coating having a thickness in therange of about 0.5 microns to about 100 microns, and is particularlyuseful as a component in magnetic applications. Preferably, the productis substantially free of metals contamination which is detrimental tomagnetic properties.

The present process provides substantial benefits. For example, theproduct obtained has manganese, zinc, iron oxide coating which hasuseful properties, e.g., outstanding magnetic and/or morphologicalproperties. This product may be employed in combination with a metalliccatalyst to promote chemical reactions, e.g., chemical oxidation or incombination with separation processes. High utilization of ferricchloride and interacting components is achieved. In addition, highcoating deposition and product throughput rates are obtained. Moreover,less rigorous conditions are employed. For example, temperatures withinsintering section 18 can be significantly less than 1100° C. to 1500° C.used in conventional processes. The product obtained has excellentstability and durability.

In FIG. 2, a rigid heating element 50 is shown. Element 50 isschematically shown in induction relating relationship to coils 52 and54 so that a field (magnetic) can be applied across element 50, inparticular across the coated substrate 56 of element 50. Referring toFIG. 3, element 50 is a flexible composite of a coated substrate 56 anda flexible, thermoplastic organic polymeric material 58. Coatedsubstrate 56 is in the form of a ceramic fiber roving, a threedimensional substrate, and provides an magnetic susceptible network inelement 50. As shown in FIG. 4, the individual coated fibers,illustrated by coated fiber 60, of coated substrate 56, are coated witha coating containing magnetic iron oxide, illustrated by coating 62 onceramic fiber 64.

Referring to FIG. 5, an alternate heating element 70 is shown. Alternateelement 70 can be used in place of element 50 in FIG. 2. Alternateelement 70 is a flexible composite of coated substrate particles 74oriented to provide a magnetic susceptible network in alternate element70, and a flexible, thermoplastic polymeric matrix material 76. Coatedsubstrate particles 74 are three dimensional particles of various sizesand shapes and are coated with a coating containing magnetic iron oxide.In cross section, each of these particles 74 looks much like individualfiber 60 in FIG. 4.

In FIG. 6, a further heating element 80 is shown. Further element 80 isshown in contact with electrical wire 82 which runs along the undersideof element 80. Further element has substantially the same structure aselement 50. As alternating electrical current is passed throughelectrical wire 82, and an alternating magnetic field is created infurther element 80. This field gives rise to small scale current loops,known as eddy currents which act to heat the further element 80resistively. The configuration shown in FIG. 6 is one embodiment of aninductive heating element in accordance with the present invention.

EXAMPLE 1

A substrate made of alumina carbide was contacted with a powder mixturecontaining ferric chloride, hexahydrate manganese dichloride, tetrahydrate and zinc chloride in a mole ratio to produce manganese, zincferrite, Mn1-xZn xFe₂₊₆ O₄. This contacting occurred at ambienttemperature in an air atmosphere at about atmospheric pressure andresulted in a coating being placed on the substrate.

This coated substrate was then heated to 285° C. and allowed to stand inan argon atmosphere at about atmospheric pressure for about 5 minutes.The coated substrate was then fired at 900° C. for 30 minutes usingflowing, at the rate of one (1) liter per minute, water saturated air atabout atmospheric pressure followed by 1 hour sintering at 1000° C. Thisresulted in a substrate having a ferrite coating with excellent magneticproperties.

The present methods and products, illustrated above, provide outstandingadvantages. For example, the iron oxide coated substrate prepared inaccordance with the present invention have improved, i.e., magneticproperties and offer significant design for a wide variety ofapplications.

EXAMPLE 2

The powder of example 1 is applied to a 26 inch by 26 inch silica fibernon woven mat in the form of a powder (10 to 125 microns in averageparticle diameter) shaken from a powder spreading apparatus positioned 2to about 5 feet above the mat. An amount of indium mono chloride powder(3 to about 70 microns in average particle diameter) is added directlyto the ferric chloride powder to provide the requisite stoichiometry forthe final iron oxide product. The powder-containing mat is placed into acoating furnace chamber at 285° C. and maintained at this temperaturefor approximately 20 minutes. During this time a downflow of 9.0 litersper minute of nitrogen heated to 350° C. to 450° C. is maintained in thechamber.

In the coating chamber the chloride powder melts and wicks along thefiber to form a uniform coating. In addition, a small cloud of metalchloride vapor can form above the mat. This is due to a small refluxingaction in which hot chloride vapors rise slightly and are then forcedback down into the mat for coating and distribution by the nitrogendownflow. This wicking and/or refluxing is believed to aid in theuniform distribution of iron chlorides in the coating chamber.

The mat is then moved into the oxidation chamber. The oxidation stepoccurs in a molecular oxygen-containing atmosphere at a temperature of900° C. for a period of time of 30 minutes followed by increasing thetemperature to 1000° for a period of time of from 10 to 1 hour. The matmay be coated by this process more than once to achieve thickercoatings.

EXAMPLE 3

Example 2 is repeated except that the powder is applied to the mat usinga powder sprayer which includes a canister for fluidizing the powder andprovides for direct injection of the powder into a spray gun. The powderis then sprayed directly on the mat, resulting in a highly uniformpowder distribution.

EXAMPLE 4

Example 2 is repeated except that the powder is applied to the mat bypulling the mat through a fluidized bed of the powder, which as anaverage particle diameter of about 5 to about 125 microns.

EXAMPLE 5 to 7

Examples 2, 3 and 4 are repeated except that, prior to contacting withthe powder, the mat is charged by passing electrostatically charged airover the mat. The powder particles are charged with an opposite chargeto that of the mat. The use of oppositely charged mat and powder acts toassist or enhance the adherence of the powder to the mat.

In each of the Examples 2 to 7, the final coated product included aneffective iron oxide-containing coating having a substantial degree ofuniformity.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An article comprising a three dimensionalinorganic substrate other than magnetic or electrically conductive ironoxide having at least one coating containing magnetic or electricallyconductive iron oxide on at least a portion of all three dimensionsthereof produced by a process comprising;contacting an inorganic threedimensional substrate which includes external surfaces and shieldedsurfaces which are at least partially shielded by other portions of saidsubstrate with a composition comprising an iron oxide forming compoundother than iron oxide at conditions effective to form an ironoxide-forming compound containing coating on at least a portion of saidsubstrate; forming a liquidus iron oxide forming compound containingcoating on at least a portion of the three dimensions of said substrateincluding the shielded surfaces of said substrate; contacting saidsubstrate with at least one additional magnetic or conductivityinteracting component at conditions effective to form acomponent-containing coating on at least a portion of said substrateincluding at least a portion of the three dimensions of said substrateincluding the shielded surfaces of said substrate; said contacting beinginitiated at least prior to the substantially complete oxidation of saidiron oxide forming compound to iron oxide; contacting said substratehaving said iron oxide forming compound containing coating and saidadditional component-containing coating thereon with an oxidizing agentat conditions effective to convert said iron oxide forming compound toiron oxide and form an iron oxide coating with additional magnetic orconductivity interacting component on at least a portion of said threedimensions of said substrate including the shielded surfaces of saidsubstrate.
 2. The article of claim 1 wherein said iron oxide formingcompound is selected from the group consisting of iron chlorides, ironsulfates, and the hydrates therefore, low molecular weight iron organiccomplexes and mixtures thereof.
 3. The article of claim 1 wherein saidiron oxide forming compound is ferric chloride hexahydrate.
 4. Thearticle of claim 1 wherein said additional component is an oxideprecursor selected from the group consisting of nickel, zinc, manganese,barium, strontium, lead, yttrium, lanthanum, calcium, boron, titanium,silica, the rare earth elements and interacting mixtures thereof.
 5. Thearticle of claim 4 wherein said additional component is an oxideprecursor selected from the group consisting of nickel, zinc andmanganese and said iron oxide forming compound is ferric chloridehexahydrate.
 6. The article of claim 1 wherein said substrate ismaintained for a period of time at conditions effective to do at leastone of the following: (1) coat a larger portion of said substrate withsaid iron oxide forming compound: (2) distribute said iron oxide formingcompound over said substrate; (3) make said iron oxide formingcompound-containing coating more uniform in thickness; (4) incorporatesaid additional interacting component in said iron oxide formingcompound coating; and (5) distribute said additional interactingcomponent more uniformly in said iron oxide forming compound containingcoating.
 7. The article of claim 1 wherein said substrates in a formselected from the group consisting of spheres, extrudates, flakes,fibers, fiber rovings, chopped fibers, fiber mats, porous substrates,irregularly shaped particles and multi-channel monoliths.
 8. The articleof claim 7 wherein said substrate is a material selected from a thegroup consisting of nickel, a glass and a ceramic oxide.
 9. The articleof claim 5 wherein said substrate is selected from the group consistingof spheres, extrudes, flakes, fibers, porous substrates, and irregularlyshaped particles.
 10. An article comprising a three dimensionalinorganic substrate other than magnetic or electrically conductive ironoxide having at least one coating containing magnetic or electricallyconductive iron oxide on at least a portion of all three dimensionsthereof produced by a process comprising;contacting an inorganic threedimensional substrate which includes external surfaces and shieldedportions of said substrate with a composition comprising a ironchloride-forming compound at conditions effective to form an ironchloride-forming compound containing coating on at least a portion ofsaid substrate; forming a liquidus iron chloride-forming compoundcontaining coating on at least a portion of the three dimensions of saidsubstrate including the shielded surfaces of said substrate and atconditions effective to do at least one of the following: (1) coat alarger portion of said substrate with said iron chloride-formingcompound (2) distribute said iron chloride-forming compound over saidsubstrate; and (3) make said iron chloride-forming compound containingcoating more uniform in thickness; contacting said substrate with saidiron chloride-forming compound containing coating with an oxidizingagent at conditions effective to convert the iron chloride-formingcompound to iron oxide and form a iron oxide coating on at least aportion of said three dimensions of said substrate including theshielded surfaces of said substrate.
 11. The article of claim 10 whichfurther comprises contacting said substrate with at least one additionalinteracting component at conditions effective to form an additionalmagnetic or conductivity interacting component containing coating onsaid substrate, said additional component contacting occurring prior tosubstantially complete oxidation of said iron chloride forming compoundto the oxide.
 12. The article of claim 11 wherein said substrate is in aform selected from the group consisting of spheres, extrudates, flakes,fibers, fiber rovings, chopped fibers, fiber mats, porous substrates,irregularly shaped particles and multi-channel monoliths.
 13. Thearticle of claim 12 wherein substrate is a material selected from thegroup consisting of nickel, a glass and a ceramic oxide.
 14. An articlecomprising a three dimensional inorganic substrate other than magneticor electrically conductive iron oxide having at least one coatingcontaining magnetic or electrically conductive iron oxide on at least aportion of all three dimensions thereof produced by a processcomprising;contacting an inorganic three dimensional substrate with acomposition comprising an iron oxide precursor powder other than ironoxide at conditions effective to form a coating containing iron oxideprecursor on at least a portion of the substrate; forming a liquidusiron oxide precursor on at least a portion of the three dimensions ofsaid substrate including the shielded surfaces of said substrate and atconditions effective to do at least one of the following: (1) coat alarger portion of said substrate with said coating containing iron oxideprecursor; (2) distribute said coating containing iron oxide precursorover said substrate; and (3) make said coating containing iron oxideprecursor more uniform in thickness; contacting said coated substratewith an oxidizing agent at conditions effective to convert said ironoxide precursor to iron oxide on at least a portion of said threedimensions of said substrate and form a substrate having an ironoxide-containing coating.
 15. The article of claim 14 which furthercomprises contacting said substrate with at least one additionalmagnetic or conductivity interacting forming component at conditionseffective to form an additional forming component containing coating onsaid substrate, said forming component contacting occurring prior to thesubstantially complete oxidation of said iron oxide precursor to ironoxide.
 16. The article of claim 14 wherein said iron oxide formingcompound is selected from the group consisting of iron chlorides, ironsulfates and the hydrates thereof, low molecular weight iron organiccomplexes and mixtures thereof.
 17. The article of claim 16 wherein saidiron oxide forming compound is ferric chloride hexahydrate.
 18. Thearticle of claim 15 wherein said additional forming component is anadditional precursor selected from the group consisting of nickel, zinc,manganese, barium, strontium, lead, the rare earth elements.
 19. Thearticle of claim 15 wherein said substrate is in a form selected fromthe group consisting of spheres, extrudates, fibers, flakes, poroussubstrates, and irregularly shaped particles.
 20. An article comprisinga three dimensional inorganic substrate other than an magnetic orelectrically conductive iron oxide having a particle type shape andwhich includes external surfaces and shielded surfaces which are atleast partially shielded by other portions of said substrate, saidsubstrate having a coating containing at least one magnetic orelectrically conductive interactant associated with the iron oxidecoating on at least a portion of said three dimensions of said substrateincluding the shielded surfaces of said substrate.
 21. The article ofclaim 20 wherein said substrate in a shape selected from the groupconsisting of spheres, extrudates, flakes, fibers, porous substrates,particles and irregularly shaped particles.
 22. The article of claim 21wherein said substrate is an inorganic oxide and in a shape selectedfrom the group consisting of spheres, extrudates, flakes, fibers, poroussubstrates, particles and irregularly shaped particles.